This invention relates to the art of anti-theft devices for motor vehicles and, more particularly, to an improved self-contained anti-theft device which can be provided in, directly attached to or otherwise mounted adjacent the battery of a motor vehicle.
The present invention provides improvements in connection with self-contained anti-theft devices of the character disclosed in U.S. Pat. No. 4,553,127 to Francis Issa and U.S. Pat. No. 5,132,551 to Louis D. Carlo et al, which patents are owned by the assignee of the present invention, and the disclosures of which are hereby incorporated herein by reference.
Each of the foregoing patents discloses a self-contained anti-theft device adapted to be mounted in or on a vehicle battery and which is operable to preclude starting of the vehicle engine when the anti-theft device is activated such as through the use of a remotely controlled encoder. More particularly, the anti-theft device comprises a power switch shiftable between first and second conditions respectively operatively connecting and disconnecting the battery to the starting circuit of the vehicle which includes a starting motor and an ignition switch. In both patents, when the anti-theft device is activated, the power switch is automatically shifted into the second condition in response to flow of a substantial amount of current from the battery indicative of an attempt to start the vehicle through use of the ignition switch or shorting thereof. In connection with such an attempt to start the vehicle, the power switch opens for a given short period of time and then closes, and repeats such opening and closing so long as the ignition switch is actuated or the short thereacross continues. Such opening and closing of the power switch precludes the delivery of sufficient current to the starting motor and provides a clicking sound which simulates the sound of a weak battery in the vehicle. This advantageously deters a would-be thief from further tampering with the vehicle in an effort to steal the same by driving it from its parked location. Through the use of the remotely controlled encoder, the power switch shifting arrangement can be disabled for a predetermined period of time, whereby the power switch will remain closed in response to actuation of the ignition switch to allow starting of the vehicle. Once started, the anti-theft device will remain in the first condition, whereby the power switch will remain closed during operation of the vehicle. In the event of a stall, the shifting arrangement is again disabled for a predetermined time so as to allow the vehicle operator to restart the vehicle without having to again actuate the encoder.
In connection with anti-theft devices operating in the foregoing manner, it has been noted that the opening and closing of the power switch in response to an unauthorized effort to start the vehicle often results in the drop out of certain pre-set electrical accessories in the vehicle, such as digital clocks and radios. In this respect, the brief interruption in the flow of current from the battery to the accessories is sufficient to cause the drop out, whereby the vehicle owner may have to reset the devices upon returning to his vehicle following the efforts of a thief to steal the same by jumping the ignition switch. While the opening and closing of the power switch and the resulting chatter simulating a weak battery serve to deter a would-be thief, having to reset digital equipment in the vehicle is an undesirable inconvenience to the vehicle owner. While the latter is apparently avoided in accordance with one embodiment in the Issa patent wherein the power switch remains open when the anti-theft device is actuated and a current limiter in parallel therewith enables continued operation of electrical accessories in the vehicle, Issa states that the current level across the limiter is high enough for various electrical devices including the vehicle lights and cigarette lighter to function normally. This, the very valuable effect of the noise simulating a weak battery in response to an effort to start the vehicle is lost with this embodiment of Issa, and if a would-be thief turns on the vehicle lights or operates other power operated accessories such as the cigarette lighter, power seats or the like, he immediately becomes aware of the fact that the battery is not the problem. Thus, the would-be thief is not likely to be deterred but, rather, will suspect the existence of an anti-theft device and thus continue to attempt to disconnect or otherwise bypass the latter. This can lead to undesirable damage to the vehicle beyond that which may occur as a result of the would-be thief entering the driving compartment of a locked vehicle and jumping the ignition switch. In this respect, for example, the thief may pry open the hood of the vehicle in an effort to locate and disable or bypass the anti-theft device, and if the thief attempts to disable the device still further damage may be done.